Acoustic Characteristics of a Propeller Experiencing Transient Disturbances in Forward and Edgewise Flight Conditions

Impact of transient disturbances on the flow and acoustic characteristics of a single propeller is investigated for both axial and edgewise flight conditions. The disturbances are generated by a flapping airfoil positioned upstream of the propeller, with the disturbance profile modulated by varying the airfoil’s maximum angle of attack and pitching actuation speed. Laser displacement sensor measurements confirmed high repeatability of the flapping mechanism. Particle Image Velocimetry (PIV) is employed to characterize the disturbance flow field at multiple measurement locations in the absence of the propeller. Subsequently, the interaction of these disturbances with the propeller is examined using individually positioned microphones. For the isolated propeller, in the edgewise configuration, baseline noise levels were dominated by broadband content and were approximately 20 dB higher than in the axial case. PIV was successfully implemented to characterize the gust, revealing that the disturbance spanned the full measurement field in the transverse direction and exhibited asymmetry about the centerline. During disturbance interaction, both configurations exhibited a broadband noise reduction followed by an increase, corresponding to variations in the mean velocity and flow angle of the incoming gust.